Main Research Findings

Phenazopyridine is a commonly used medication to relieve pain associated with urinary tract infections, such as cystitis. However, recent studies have revealed serious side effects associated with phenazopyridine use. 6 reports that phenazopyridine can cause acute interstitial nephritis, a serious side effect that causes inflammation of the kidneys. Additionally, 2 indicates that prolonged use of phenazopyridine can lead to Heinz body hemolysis, a condition that causes destruction of red blood cells. Furthermore, 7 reports that phenazopyridine can cause methemoglobinemia, a condition that reduces the oxygen carrying capacity of the blood.

Reasons for Side Effects

The exact reasons for phenazopyridine's side effects are not fully understood. However, several studies suggest that a substance called 2,3,6-triaminopyridine, produced when phenazopyridine is metabolized in the body, may generate reactive oxygen species, causing damage to cells. 8 reports that 2,3,6-triaminopyridine can produce superoxide radical and hydrogen peroxide, causing oxidative stress to red blood cells. Additionally, phenazopyridine can affect kidney function by directly damaging kidney cells or by causing pigment-induced nephropathy resulting from red blood cell destruction. 6

Common Side Effects

Urine discoloration

Phenazopyridine often causes urine to turn orange. This is due to the drug being excreted in urine. This side effect is usually harmless. 6

Skin discoloration

Phenazopyridine can cause skin to turn yellow. This is due to the drug depositing in the skin. This side effect is usually harmless. 6

Gastrointestinal side effects

Phenazopyridine can cause gastrointestinal side effects such as stomach pain, nausea, vomiting, and diarrhea. 6

Methemoglobinemia

Phenazopyridine can cause methemoglobinemia. Methemoglobinemia is a condition that reduces the oxygen-carrying capacity of the blood. Symptoms of methemoglobinemia include shortness of breath, headache, dizziness, and a bluish appearance. 7

Acute interstitial nephritis

Phenazopyridine can cause acute interstitial nephritis. Acute interstitial nephritis is a condition that causes inflammation of the kidneys. Symptoms of acute interstitial nephritis include fever, back pain, decreased urine output, and changes in urine color. 6

Heinz body hemolysis

Phenazopyridine can cause Heinz body hemolysis. Heinz body hemolysis is a condition that causes destruction of red blood cells. Symptoms of Heinz body hemolysis include anemia, jaundice, and fatigue. 2

Skin ulcers

Phenazopyridine can cause skin ulcers. This is due to an allergic reaction to the drug. 5

Sulfhemoglobinemia

Phenazopyridine can cause sulfhemoglobinemia. Sulfhemoglobinemia is a rare dyshemoglobinemia that presents similarly to methemoglobinemia. 1

Side Effects Management

Methemoglobinemia

Treatment for methemoglobinemia includes medications such as methylene blue. 3

Acute interstitial nephritis

Treatment for acute interstitial nephritis includes medications such as steroids. 6

Skin ulcers

Treatment for skin ulcers includes antibiotics and special dressings. 5

Comparison Across Studies

Commonalities

Many studies indicate that phenazopyridine can cause serious side effects. These side effects include methemoglobinemia, acute interstitial nephritis, Heinz body hemolysis, and skin ulcers.

Differences

Several studies indicate an increased risk of certain side effects with phenazopyridine. For example, 7 shows an increased risk of methemoglobinemia in patients with kidney failure, elderly individuals, and those who overdose. Additionally, 2 indicates an increased risk of Heinz body hemolysis in patients who have received hematopoietic stem cell transplants.

Practical Implications

While phenazopyridine has pain-relieving effects, it can also cause serious side effects. It is important to follow your doctor's instructions when taking phenazopyridine. Consult your doctor before taking phenazopyridine, particularly if you are elderly, have kidney failure, or are at risk of overdosing, or if you have received a hematopoietic stem cell transplant.

Limitations of Current Research

Currently, there is limited data on phenazopyridine's side effects. Additionally, these studies focus on specific population groups and may not apply to all patients.

Future Research Directions

Further research on phenazopyridine's side effects is necessary. In particular, it is important to investigate how phenazopyridine affects specific population groups. It is also essential to develop methods to reduce phenazopyridine's side effects.

Conclusion

While phenazopyridine can relieve pain, it can also cause serious side effects. It is important to follow your doctor's instructions when taking phenazopyridine. If you are concerned about side effects, consult your doctor.